Effects of point source pollution on water quality, phytoplankton diversity and abundance in lake Victoria, Kenya

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Water quality deterioration remains a major problem in most fresh water lakes. This study was conducted to establish the extent of water quality deterioration in Kisumu Bay of Winam Gulf, Lake Victoria. The overall objective was to assess the effects of point source pollution on water quality and phytoplankton community structure. Sampling stations were selected randomly all over the bay and marked with a global positioning system (G.P.S). Triplicate samples of dissolved oxygen concentration, conductivity, ammonia, nutrients, chlorophyll-a and phytoplankton were taken for laboratory analysis. Mean overall dissolved oxygen concentration was 7.41±1.39 mg l-1. Mean conductivity level was 142.39±63.786 µScm-1 whereas mean soluble reactive phosphorus level was 330.02±311.9 mg l-1. The mean overall chlorophyll a level was 592.9± 604.4 mg l-1 indicating that the bay is eutrophic. The Duncan multiplernrange test showed significant variability of the means of this parameters at different sampling sites at p=0.005. At 46%, the diatoms were the most dominant phytoplankton family in the bay. There were significant differences in distribution of different phytoplankton taxa at different sampling sites (p=0.0001). The results of this study can be used to formulate management options for the improvement of water quality in the Kisumu Bay of Lake Victoria.